In fiction, one of the easiest ways to incapacitate an opponent or group of opponents is to get them in a closed room and pump in Knockout Gas. Knockout Gas is an area-effect form of InstantSedation: as soon as the victims breathe it, they cough weakly a few times and then slump to the floor unconscious.

Usually delivered as a visible fog, and often [[TechnicolorScience brightly colored]] as well, but invisible gas is also common, particularly in budget-conscious productions. Knockout Gas can be delivered through special vents just for that purpose, or it can be pumped in through the regular ventilation system. As with other forms of InstantSedation, dosage doesn't seem to matter. The effects last just long enough for maximum tension or drama. Recovery tends to be just as fast as the onset, and the victims rarely suffer any lasting effects beyond, perhaps, a mild headache. Nobody ever seems to crack their skull or otherwise get hurt when falling down, either.

Frequently employed by villains, but also a convenient weapon for heroes due to its non-lethal nature.

Subtrope of InstantSedation, and related to OneDoseFitsAll. SisterTrope to DeadlyGas (and in RealLife, though almost never in fiction, the line between the two can be a very fine one.) SisterTrope to TranquillizerDart.

Though anaesthetic and hypnotic gasses of many sorts exist, all have the properties of being fairly slow-acting, decidedly dosage-dependent, and fairly easily lethal, unlike the gasses in this trope. Therefore, please refrain from citing real life examples.----!!Examples

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[[folder:Anime & Manga]]* [[ColdSniper Dieci]] in ''Anime/MagicalGirlLyricalNanohaStrikerS'' has the [[AbnormalAmmo Aerosol Shell]] of her [[{{BFG}} Enormous Cannon]], which releases fast-acting knockout gas after they explode on impact as shown during the assault on the Ground Forces HQ. Unlike [[TechnicolorScience the more colorful gases used in many other media]], these have the appearance of ordinary white smoke.** In ''NanohaForce'', Arnage's knockout gas has so far been the only thing to reliably stop Reacted Thoma's rampage.* ''Anime/CowboyBebop'' episode 8 "Waltz for Venus". During a hijacking, Faye renders a female hijacker unconscious with a spray of vapor.* Used a lot by Manga/{{Genzo}}, with the gas usually stored in his puppets.* In Manga/OnePiece, half of the Straw Hats fall victim to this whilst the others are exploring Punk Hazard. The ArcVillain Caesar Clown also uses a variation of the trope. He doesn't knock out people with gas, but rather ''lack'' of gas: he uses his powers to take away all of the oxygen from a specific area, and thus suffocates the opponent to unconsciousness.* One of Kaito Kid's tricks in ''MagicKaito'', as seen used in the OVA.* In ''DragonBall'' when Goku and friends are captured by Emperor Pilaf he floods their prison with sleeping gas to knock them out so he can search for the remaining dragon ball they have while they're all unconscious and can't do anything. [[TooDumbToLive He then enters the chamber before the gas has begun clearing out and knocks himself out too.]][[/folder]]

[[folder:Comic Books]]* One of the most consistent ways of defeating TheHulk, at least on those occasions when he doesn't remember that he can hold his breath for hours. As the Hulk isn't all that bright, this is not infrequent.* {{Hawkeye}} uses trick arrows, one of which, is a knock-out gas arrow.* Franchise/{{Batman}} has used knockout gas from various sources: bombs, canisters, guns, etc.* As with the movie and TV versions, the comic versions of Franchise/TheGreenHornet have also used knock out gas.* Enemies of ''{{Spider-Man}}'' have used it from time to time. Mysterio, Kraven, the Chameleon, the Hobgoblins, and [[NormanOsborn Green Goblins]] are all culprits.* DCComics' golden age hero [[SandManMysteryTheatre Sandman]] used a knockout gas gun. Later versions of the character also used knock out gas.* In ''Amazing {{Spider-Man}}'' #661, Veil turns into isoflurane, an anesthetic gas, to keep two muggers down. True to the usual depiction, despite the gas generally being colorless, it appears as a thick fog.* In ''Comicbook/JetDream'', Jet uses "Kayo Powder" [[ShoePhone in a makeup compact]] for this effect.* In ''{{Tintin}} in America'', the Gangsters Syndicate of Chicago uses knockout gas on Tintin after dropping him through a TrapDoor and before dumping him into Lake Michigan. Fortunately for Tintin, they used the wrong kind of gas.* In ''Comicbook/AmericanFlagg'', Somnabutol™, in low doses, is a recreational drug. In higher doses, it's "the Official Riot Control Device of the 1996 East Coast Meltdown." Also described as "like a wet dream without the hot parts."* In ''[[Comicbook/XMen The Uncanny X-Men]]'', in one issue, Cyclops is being chased by the rest of the X-Men who have been tricked by [[spoiler:Mastermind]] into thinking he's [[spoiler:Dark Phoenix]] come back to life. He lures the X-Men into the Danger Room, where he uses a field of "Wizard of Oz" poppies keyed specifically to knock Rogue unconscious. He does this so that he can [[spoiler:use her power absorption power to take brief control of a comatose Professor X's psionics to pierce Mastermind's illusion]].[[/folder]]

[[folder:Fan Works]]* ''Fanfic/CalvinAndHobbesTheSeries'':** Used by [[MoralityDial Evil Jack]] on Calvin and Hobbes in "62 Percent More Evil". It comes in a deodorant can.--> "Designed to render unconscious and keep you smelling like pine for at least two hours."** Sherman later uses it on Andy's parents in "Dark Laughter".[[/folder]]

[[folder:Films -- Animation]]* The short film ''Anime/{{Interstella 5555}}'' that goes with the Music/DaftPunk album ''Discovery'' starts off with an entire stadium full of concert-goers subdued by black-suited mooks with devices that shoot pink gas. The entire stadium goes down in seconds. The one person who escapes is taken down with a specialized crossbow bolt whose head bursts into a similar cloud of pink smoke.* WesternAnimation/{{Megamind}}'s Minion possesses a Knockout Aerosol can, which he mostly uses on Roxanne in her endless kidnappings. Halfway through the film he [[CrowningMomentOfFunny runs out of it]] and resorts to [[TapOnTheHead Forget-Me-Stick]].[[/folder]]

[[folder:Films -- Live-Action]]* In TheFilmOfTheSeries of ''Film/TheAvengers1998'' Father knocks Mrs. Peel out instantly with gas from an aerosol can.* In 1966's ''Film/BatmanTheMovie'', Batman and the Penguin each use a gas that causes instant unconsciousness (called Bat-Gas and Penguin Gas, respectively).* ''Film/DiamondsAreForever''. While Film/JamesBond is in Willard Whyte's elevator, Blofeld renders him unconscious with knockout gas.* Britt's iconic Gas Gun in the 2011 ''Film/TheGreenHornet'' film. It instantly puts anyone to sleep for about an hour, though this was only after Kato experimented with and perfected it. The first mixture put Britt out for eleven days.-->'''Britt:''' I was out for eleven days?! I wasn't asleep, that was a coma, you dick! Did you put this diaper on me?!* In ''Film/{{Help}}'', a sinister red gas takes out all of the [[BritishRoyalGuard Buckingham Palace guards]] in a matter of seconds.-->'''Ringo:''' It must be their tea break.* In ''[[Film/TheHungerGamesMockingjay The Hunger Games: Mockingjay Part 1]]'', the rebel team [[spoiler:sent to rescue the Victors]] uses sleeping gas bombs to clear areas before they enter. [[spoiler:Peeta gets knocked out by the gas as well, and comes to in the hospital at District 13]].* ''Film/MysteryMen'' has [[JerkJock Captain Amazing]] fall victim to [[EvilGenius Casanova Frankenstein's]] fiendishly clever [[SchmuckBait Chloroform-Deploying Enticement Snare]]. * Even the great ElSanto proves vulnerable to a knockout gas grenade thrown by a hunchback in ''Film/SantoYBlueDemonContraDraculaYElHombreLobo''.* ''Film/StrangePsychokineticStrategy'' had yellow smoke knocking out half a dozen police, from a cymbal-smashing monkey. * Played with in the 1967 comedy ''ThoroughlyModernMillie'' where the antagonist is pumping a white sleeping gas into the room of someone she plans to kidnap and sell into slavery, the problem is that she is in the room with the gas. As the gas gets thicker in the room she starts to yawn, slows down, and finally just falls over onto the bed; the gas has dissipated by the time she is found, still asleep. It is then later played straight with darts that work instantly.* Artemus Gordon's sleeping gas billiard balls in ''Film/WildWildWest''. The logic of having sleeping gas disguised as a billiard ball is {{lampshaded}} by Jim.-->'''West:''' Well I don't know about you, but I'm certainly gonna sleep better, assuming Loveless barges in here and wants to play a game of pool.** Except for the 8-ball, which is an incendiary bomb. * In ''Film/CloseEncountersOfTheThirdKind'', the Army douses the Devil's Tower mountain with sleeping gas to prevent any unevacuated civilians from setting eyes on the UFO landing zone. Jillian and Roy manage to escape it, but Larry succumbs.* In OldDarkHouse horror comedy ''Film/TheMonster'', the room that Johnny, Amos, and Betty are in has a fireplace that starts emitting knockout gas. Johnny and Amos escape, but Betty is captured when the bed she's lying on turns out to be a trap that's lowered into the basement.* Ethan suffers from this after receiving a taunting briefing from the Syndicate in ''Film/MissionImpossibleRogueNation'', but not before witnessing [[BigBad Solomon Lane]] executing a shop girl. [[spoiler: Later, Ethan does almost the exact same thing to Lane, and then arrests him.]]* The [[UtopiaJustifiesTheMeans Gas of Peace]] in ''Film/ThingsToCome'', except for the warlord who fails to realise the benefits of OneWorldOrder and conveniently dies of a heart attack after inhaling it.[[/folder]]

[[folder:Gamebooks]]* ''Literature/LoneWolf'' features knockout gas in ''Castle Death'', filling some trapped rooms or delivered by an ugly dwarf blowing it in your face through a brass tube.[[/folder]]

[[folder:Literature]]* Franchise/DocSavage used anesthetic gas grenades. Somewhat justified in that Doc was supposed to have specifically invented these.** In ''Fear Cay'', one of the Franchise/DocSavage novels, the bad guys try to capture Doc with Knockout Gas dispensed from a rigged wallet left on the sidewalk where he would find it. It doesn't work, because of his superior ability to smell ([[FridgeLogic he somehow smelled it before he breathed it]]) and (as with TheHulk) his ability to hold his breath for much longer than normal. In this case it was ''not'' visible.* The Alistair [=MacLean=] novel ''The Golden Gate'' has aerosol gas that cause instant unconsciousness.* Subverted in the opening scene of ''A Piece of Resistance'' by Clive Egleton. LaResistance use a knockout gas to remove an innocent bystander, who then dies of a heart attack.* ''Fighting Slave of Literature/{{Gor}}'': Jason Marshall and his date Beverly are taken out by knockout gas in the backseat of a specially-prepared taxi. They were only after her, but he forced his way into the cab when she was trying to end the date.* In Creator/HarryHarrison's ''Literature/TheStainlessSteelRat'' series, both local law enforcement and Slippery Jim use Knock-out Gas with great abandon, although slightly more realistically than is usual in fiction. Jim makes sure to use nasal filters or a mask to avoid breathing it in himself, it's usually invisible rather than brightly coloured, and there are numerous different types, with different effects, speed of action, duration and after-effects.* In Creator/LarryNiven and Jerry Pournelle's ''Oath of Fealty'', The Todos Santos arcology uses knockout gas as part of its internal security system.* In ''Literature/LittleGreenMen'', the "aliens" use a gas named sevoflurane to anesthetize their abductees, usually with added ammonia and cinnamon scent.* Anne McCaffery's ''Pegasus'' series has Law Enforcement & Order use 'anesthesine gas'.[[/folder]]

[[folder:Live-Action TV]]* ''Franchise/TheGreenHornet'' has as one as his main weapons, the "Hornet gun", spraying "Hornet gas" that would knock out mooks with one sniff. This is a carryover from the original radio series and 1940s film serials.* ''Series/ThePrisoner''. The sleeping gas used on Number 6 in his apartment in the first episode (and each episode's opening title).* A constantly-recurring staple of both villains and heroes on ''Series/{{Batman}}'', most often in the form of colorful Knockout Gas.** "The Bookworm Turns". The sleeping gas released by the Bookworm's booby-trapped book renders Robin unconscious in seconds.** "While Gotham City Burns". The Bookworm uses a package booby-trapped with sleep gas to render Alfred and Aunt Harriet unconscious so he can steal a book from the Wayne manor library.** In "Hi Diddle Diddle" and "Smack in the Middle" the Riddler uses a aerosol can of sleeping gas to put Robin to sleep.** "The Ring of Wax". The Riddler renders a guard unconscious with gas released from a candle.* ''SimonAndSimon'' episode "Under the Knife" has A.J. gassed in a hospital room and in danger of unnecessary surgery when the brothers get too close to the truth in a malpractice scam.* ''Series/StarTrekTheOriginalSeries'' episode "Space Seed". After Khan takes over the Enterprise, Kirk orders that all decks be flooded with Neural Gas, which would render everyone aboard unconscious. That attempt fails, but later the attempt succeeds.* In ''Series/WonderWoman'' season 1 episode "Judgment from Outer Space (Part 1)": she's taken down by knockout gas.* ''Series/TheWildWildWest''** In the episode "The Night of the Sudden Death", invisible gas pumped in from a gaslight lamp [[AndSomeOtherStuff with an unspecified additive]] is used to fill a very large U.S. Mint set and knock out several people within seconds.** In another episode, Gordon uses Knockout Gas himself, but he's still dissatisfied with it because it's too visible.* In the "Biology 101" episode of ''Series/{{Community}}'', a variant of Knockout Gas intended for monkeys ("Chimpan-Zzz" brand) is pumped into the Greendale air vents. It turns out to work on humans too, with the additional side effects of causing hallucinations and references to ''Film/TwoThousandOneASpaceOdyssey''.* In the ''Series/StargateAtlantis'' episode "Inquisition", Atlantis' first team is taken out by Knockout Gas in a cell, before being moved to another planet through the Stargate so the rest of the expedition can't find them.* In ''TheAquabatsSuperShow'' episode "Cobraman!", while the team is trapped inside the Battletram by Carl, who forces the team to watch the MC Bat Commander fight the Cobraman, Jimmy the Robot detaches one of his hands and remote controls it so as to access a knockout gas button that, when activated, knocks out Carl and the rest of the team inside (Jimmy, being a robot, isn't affected by the gas), effectively freeing the team from Carl's clutches.* Skouras tries to use this (or possibly DeadlyGas, but the fact that he had henchmen in gas masks with guns on hand suggests that the gas itself wouldn't have killed her) on Dani in the finale of ''Series/{{Believe}}''. She manages to neutralize it with her PsychicPowers, something that even with all of his years studying people like her he didn't think was possible.* ''Series/MacGyver'': An instantly sedating knockout gas was one of the weapon systems on the attack helicopter in "Honest Abe".[[/folder]]

[[folder:Tabletop Games]]* ''TabletopGame/DungeonsAndDragons''.** At the end of module A3 ''Assault on the Aerie of the Slave Lords'', a green gas (the "Smoke of the Little Death") is used to knock out the {{PC}}s so they can start the next module as the Slave Lords' prisoners.** In module S1 ''Tomb of Horrors'', there's an area filled with sleep gas. Everyone who enters the corridor immediately falls asleep for between 20 minutes and more than an hour, during which time they will probably be squashed flat by the magical equivalent of a steamroller.** Module S3 ''Expedition to the Barrier Peaks'' has sleep gas grenades. Anyone exposed to their gas falls asleep for 20-50 minutes.* ''TabletopGame/{{Shadowrun}}''. The various Neurostun gasses are often used to take out shadowrunners without killing them.* Judges Guild supplement ''Revised Guide to the City State''. The Temple of Bubastis has a huge hollow brass idol with a 4th level magic user inside it. Worshippers drop treasure before the idol and then leave. If they return too soon, the magic user will pull a lever and fill the area with sleeping gas.* ''TabletopGame/{{Traveller}}''** Double Adventure 3 ''Death Station''. One of the items of equipment available to {{PC}}s was Tranq Spray, a small aerosol can that sprayed a tranquilizing mist. When used at close range, it calmed the target down and then put it to sleep.** Adventure 8 ''Prison Planet''. The guards in the Imperial prison on Newcomb can release knockout gas to neutralize rioting inmates. The gas is not stopped by a standard filter mask.* ''TabletopGame/MarvelSuperHeroes'' supplement ''Uncanny X-Men'' boxed set "Adventure Book".** In chapter 4 "Time Out" the {{PC}}s are at a charity basketball game when the supervillain Arcade performs a KnockoutAmbush by flooding the gymnasium with sleep gas in order to capture them.** At the end of Chapter 8 "Terror in the Amazon" the {{PC}}s are subjected to another KnockOutAmbush by Arcade's sleep gas the same way they were in Chapter 4.* Gas Grenades are a weapon that can be used by the crew-player in the boardgame ''TabletopGame/TheAwfulGreenThingsFromOuterSpace''; the effect on the Things (good, bad or indifferent) is randomly determined for each game, but any crew present when one gets set off are knocked unconscious for a turn.* ''TabletopGame/{{Champions}}'' Organization Book 2 ''PRIMUS and DEMON''. Demonflux tries to capture the superhero Sureswift by luring him into a warehouse and flooding it with a sickly-sweet gas that causes unconsciousness.* ''TabletopGame/TopSecret Companion'', adventure "Operation Meltdown". There are two sleep gas traps in the houses occupied by the main villains that render anyone without appropriate protection unconscious.** In an elevator, pushing one of the buttons releases sleeping gas through vents in the ceiling.** A secure vault will release sleep gas if one of the necessary combinations to open it is not entered correctly.[[/folder]]

[[folder:Theatre]]* In ''Theatre/AnimalCrackers'', when Doucet threatens to arrest people unless they produce the painting, the Professor sprays everyone else with knockout gas, and after lying down beside a girl sprays himself. For no particular reason, this became the ending of the film version.[[/folder]]

[[folder:Video Games]]* ''VideoGame/{{Thief}}'' has Gas Arrows: shooting a mook will knock him out even if he's fully aware of your presence (and thus would only get annoyed by the Blackjack). Shooting the ground has an area effect, knocking out everyone within a meter or so.* ''VideoGame/DeusExHumanRevolution'' has Gas Grenades as one of the weapons in the pacifist player's arsenal. It's a generally useful tool for knocking out multiple enemies where tranqs, stun guns, and takedowns are just inappropriate, and everything else is overly lethal.* In the Apple II-era game ''[[http://en.wikipedia.org/wiki/Infiltrator Infiltrator]]'' and ''Infiltrator II'', you use a canister of knock-out gas to deal with enemy {{mooks}} (and I don't mean hitting them with the can). Works instantaneously every time.* The ''VideoGame/RuneScape'' quest "The Great Brain Robbery" has a section where Harmony Island is covered in knockout gas. You have to wear a scuba-diving helmet or you'll be knocked unconscious.* In ''VideoGame/MegamanBattleNetwork 5'', at the very beginning of the game, Lan, Dex, Mayl, Yai, and Yuuchiro are knocked out with bright pink sleeping gas, Yuuchiro is kidnapped, and everyone's navis except Megaman are stolen.* In ''SonicAdventure'', Eggman gives Sonic and Tails a quick snort of purple sleeping gas outside the casino. Puts 'em under in seconds flat, too!* The later ''SyphonFilter'' games have [=DormaGen=] gas grenades.[[/folder]]

[[folder:Visual Novels]]* In VisualNovel/NineHoursNinePersonsNineDoors and it's sequel, VisualNovel/VirtuesLastReward, the main characters are all sedated with a gas called Soporil, after which they are kidnapped to play the Nonary Game.** In the first game it's a huge plot point that it works like this. Pretty much it the first anesthetic gas that you don't have to dose properly to avoid overdose.[[/folder]]

[[folder:Web Comics]]* Used occasionally by [[EmperorScientist Klaus Wulfenbach]] in ''Webcomic/GirlGenius''.[[/folder]]

[[folder:Western Animation]]* WesternAnimation/BatmanTheAnimatedSeries: ''Magazine/{{MAD}}'' parodied the tendency of villains to use this.-->Bats-man: "Cattywoman's releasing some horrible gas!"-->Robin (drawn to look like [[ComicStrip/CalvinAndHobbes Calvin]]): "That might be me, Bats-Man. We did stop at '''Taco Bell'''!"* WesternAnimation/TheSimpsons: In ''Treehouse of Horror III: King Homer'', the giant ape is subdued by KnockOutGas, but not before eating someone.* ''WesternAnimation/JonnyQuest'' TOS episode "The Quetong Missile Mystery". Sleep gas knocks out General Fong in a couple of seconds.* ''WesternAnimation/FamilyGuy'' Peter gave his rival a statue of himself that sprayed "Crazy Purple Knockout Gas!"* ''[[WesternAnimation/SheRaPrincessOfPower She-Ra: Princess of Power]]'' once features a scene where villain Hordak sprays one of the heroes with some sleep gas from his [[SwissArmyAppendage Swiss Army Hand]]. The hero gets off an exclamation and keels over. Hordak then comments that he's going to have to have a word with his scientists; the victim shouldn't have had time to say anything before succumbing.** Shadow Weaver also uses spells that consist of "sleep mist" which is magical KnockOutGas.* ''WesternAnimation/HeManAndTheMastersOfTheUniverse1983'': Skeletor has spells that function as this.* ''SpaceGhost'' episode "The Looters". Brak uses a sleep gas missile on a ship.* In one of the Music/{{Gorillaz}} short animated idents, 2D is knocked out cold by [[http://www.youtube.com/watch?v=3lrvdbQFI2w just a whiff of gas.]]* ''WesternAnimation/DarkwingDuck'' uses a gun that could fire knock out gas (among other things). Due to the character being a little clumsy, he knocks himself out once or twice.* In ''WesternAnimation/{{Wakfu}}'' season 2, the [[HeroAntagonist Justice Knight]] captures fugitives with his [[{{Thememobile}} Justice Train]] by trapping them inside the wagon, which then fills with a golden Knockout Gas. The effects are shown to be immediate even with the heroes.* Subverted in ''WesternAnimation/{{Archer}}'', when Cyril thinks he's delivering a dose:-->'''Cyril:''' ''(procuring a [[BriefcaseFullOfMoney briefcase]]'' I got the ten million in bearer bonds.\\'''Spelvin:''' Unbelievable!\\'''Cyril:''' Well, I...\\'''Spelvin:''' No, I mean literally. I don't believe you. I suppose this is full of knockout gas or something... ''(opens briefcase to reveal a single cupcake)''\\'''Cyril:''' Apparently not.\\'''Archer:''' ''(kicking in the door)'' Exactly! Because I don't know if that's even a real thing!* One of WesternAnimation/KimPossible's gadgets is [[ShoePhone a "lip gloss" container]] that actually holds a [[StinkBomb "super-stink" formula]] created by [[MissionControl Wade]] using [[SmellyFeet his dad's dirty socks]].* The ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' episode "[[Recap/MyLittlePonyFriendshipIsMagicS2E24MysteryOnTheFriendshipExpress MMMystery on the Friendship Express]]" has the cake-guarding Pinkie Pie taken out with this by a [[TuxedoAndMartini Tuxedo-and-Martini]] superspy in one of Pinkie's {{Imagine Spot}}s.* One of the many types of gases used by the vile borg, Noxious in ''WesternAnimation/SkysurferStrikeForce''.* ''[[WesternAnimation/{{Birdman}} The Galaxy Trio]]'' episode "The Duplitrons". Meteor Man is taken out twice by sleep gas: once while he's flying in a rocket pod, the second time after he wakes up in the Duplitrons' base.* ''WesternAnimation/FantasticVoyage''. At the beginning of "The Master Spy" the title character knocks out Professor Carter by using a gas gun to fire sleeping gas into his face.[[/folder]]----